Video display systems generally display an image in arrays of pixels. Among various video display systems, an optical projection system is known in the art to be capable of providing a high quality video display in a large scale. In one particular optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N actuated mirrors, wherein each of the M.times.N mirrors is coupled with each of the M.times.N actuators. The actuators are made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to electrical signals applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as projection lens, thereby offering a displayed image thereon.
The present invention concerns primarily with a method for fabricating and mounting an array of M.times.N mirrors on an array of M.times.N electrodisplacive actuators to thereby form an array of M.times.N electrodisplacive actuated mirrors for use in the optical projection system described above.
There are illustrated in FIGS. 1A to 1F one of the conventional fabrication processing sequences of an array of M.times.N mirrors. It involves, first, as shown in FIG. 1A, formation of a separation layer 3 on a flat top surface of a substrate 1. The formation of the separation layer 3 is carried out by spin-coating of a photoresist. Then a first metallic layer 5 is deposited on top of the separation layer 3 by using, e.g., sputtering. The first metallic layer 5 is for reflecting incident light beams and is made of a light reflecting metal such as aluminum (Al). Subsequently, a second and a third metalliclic layers 6,7 are applied on the first metalliclic layer 5 by using a similar technigne used in the formation of the first layer 5. The second metallic layer 6 functions as an intermediate layer for conferring good adhesivity between the first metallic layer 5 and the third metallic layer 7. Copper (Cu) and nickel(Ni) are commonly used for the second layer 6 and the third metallic layer 7, respectively.
In the subsequent step, the metallic layers 5,6,7 are patterned into an M.times.N mirror array structure 20 by employing a conventional photolithography process, as shown in FIG. 1B. In the following step as shown in FIG. 1C, a photoresist layer 11, composed of the same photoresist as used in the separation layer 3, is applied onto the structure treated in FIGS. 1A to 1B, and subsequently defined for exposing the top surface of the third metallic layer 7. The exposed surface acts as a seed in the following electroplating process.
Thereafter, a fourth metallic layer 13, composed of the same metallic as the one used in the forming of the third metallic layer 7, is electroplated, as shown in FIG. 1D, on the surface of the third metallic layer 7 not covered by the photoresist layer 11. An M.times.N actuator array 15 is then bonded on the surface of the fourth metallic layer 13 such that each of the actuators, e.g., 17, in the M.times.N actuator array 15 is aligned with each of the M.times.N mirrors in the M.times.N mirror array structure 20 as shown in FIG. 1E, wherein each of the M.times.N mirrors is comprised of the metallic layers 5,6,7 and 13.
The photoresist layer 11 is then removed with the separation layer 3 concurrently to thereby disengage the substrate 1; and the formation of the M.times.N mirror array 21 is finalized as shown in FIG. 1F. The fourth metallic layer 13 serves as a supporting layer for preventing the first metallic layer 5, which has a substantially larger surface area than that of the actuator, from sagging; and, therefore, the formation of the fourth metallic layer 13 is carried out by such an electroplating technique that can provide a sufficient thickness for such purpose.
In the above-described fabrication process for an M.times.N mirror array 21, as illustrated in FIGS. 1A to 1F, it involves the formation of multiple metalliclic layers, including a cumbersome electroplating process; and, therefore, the processing steps tend to be complicated and costly.